Coplanar process fluid pressure sensor module

ABSTRACT

A coplanar process fluid pressure sensor module is provided. The module includes a coplanar base and a housing body. The coplanar base has a pair of process fluid pressure inlets, each having an isolator diaphragm. The housing body is coupled to the coplanar base at an interface between the coplanar base and the housing body. A differential pressure sensor is operably coupled to the pair of process fluid pressure inlets, and is disposed proximate the coplanar base within the housing body.

BACKGROUND

A process transmitter generally includes a transducer or sensor thatresponds to a process variable. A process variable generally refers to achemical or physical state of matter or conversion of energy. Examplesof process variables include pressure, temperature, flow, conductivity,pH, and other properties. Pressure is considered to be a basic processvariable in that it can be used to measure flow, level, and eventemperature.

Pressure transmitters are commonly used in industrial processes tomeasure and monitor pressures of various industrial process fluids, suchas slurries, liquids, vapors, and gases of chemical, pulp, petroleum,gas, pharmaceuticals, food, and other fluid-type processing plants.Differential pressure transmitters generally include a pair of processpressure fluid inputs which are operably coupled to a differentialpressure sensor (within the transmitter) that responds to the differencein pressure between the two inputs. Differential pressure transmitterstypically include a differential pressure sensor operably coupled to apair of isolator diaphragms. The isolator diaphragms are positioned atthe process fluid inlets and isolate the differential pressure sensorfrom the harsh process fluids being sensed. Pressure is transferred fromthe process fluid to the differential pressure sensor through asubstantially incompressible fill fluid carried in a passagewayextending from the isolator diaphragm to the differential pressuresensor.

Process fluid pressure transmitters are generally coupled to the processvia an instrument manifold or flange. One type of arrangement providesan instrument manifold that presents the process fluid pressure inletsin a pair of substantially coplanar ports. One example of such amanifold is sold under the trade designation Model 305 Coplanar™available from Rosemount Inc., of Chanhassen, Minn. The coplanar designenables flangeless valve integration, and generally provides a compact,light-weight assembly. Moreover, the coplanar design facilitatesin-process calibration, and provides substantially fewer possible leakpoints than conventional non-planar manifold-transmitter assemblies.

A process fluid pressure transmitter is generally considered a fielddevice and that it is able to be mounted in the field. “Field” isgenerally an external area in a process installation that may be subjectto climatological extremes, vibration, changes in humidity,electromagnetic or radiofrequency interface, or other environmentalchallenges. Thus, the robust physical package of a process fluidpressure transmitter provides the transmitter with the ability tooperate in the “field” for extended periods (such as years) at a time.

SUMMARY

A coplanar process fluid pressure sensor module is provided. The moduleincludes a coplanar base and a housing body. The coplanar base has apair of process fluid pressure inlets, each having an isolatordiaphragm. The housing body is coupled to the coplanar base at aninterface between the coplanar base and the housing body. A differentialpressure sensor is operably coupled to the pair of process fluidpressure inlets, and is disposed proximate the coplanar base within thehousing body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a front view of an exemplary PRIOR ART pressuretransmitter.

FIG. 2 illustrates an oblique sectional view of a module housing.

FIG. 3 is diagrammatic perspective view of a prior art coplanar pressuresensor module and a flange in accordance with the prior art.

FIG. 4 illustrates an exploded diagrammatic perspective view of animproved coplanar pressure sensor module in accordance with theembodiments of the present invention.

FIG. 5 is a cross sectional diagrammatic view of a coplanar pressuresensor module in accordance with another embodiment of the presentinvention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIG. 1 illustrates a front view of an exemplary PRIOR ART pressuretransmitter 100. Pressure transmitter 100 includes an electronicshousing 101 that encloses electronic circuitry and a pressure sensormodule housing 102 that houses isolator diaphragms, a pressure sensorand associated sensor circuitry. Pressure sensor module housing 102 isbolted to a pressure flange 104 by bolts 105. The bolts 105 also passthrough flange adapter unions 118. Flange adapter unions 118 havethreaded inlets which are connectable to threaded process pipes (notillustrated). Pressure flange 104 provides one or more process fluidspressures to the transmitter 100 for pressure measurement. Pressuretransmitter 100 is connected to process loop 103 that energizes pressuretransmitter 100 and provides bidirectional communication for use in aprocess control system.

Pressure sensor module housing 102 includes isolator diaphragms 110(shown in FIG. 2) that are welded directly to pressure sensor modulehousing 102. Housing 102 also includes threaded bolt holes 112 in astandard pattern around isolator diaphragms 110.

FIG. 2 illustrates an oblique sectional view of pressure sensor modulehousing 102. Differential pressure sensor 140 is located inside pressuresensor module housing 102 and connects, by tubes 142, 144, to isolatordiaphragms 110. Isolator diaphragms 110 are welded directly to pressuresensor module housing 102. A circuit board 146 provides circuitryassociated with processing electrical signals from differential pressuresensor 140. Flat cable reel 148 houses a flat cable that provideselectrical connections from circuit board 146 to circuitry in anelectronics housing (such as housing 101 shown in FIG. 1).

The coplanar pressure sensor module is a significant contributor to theoverall cost of the final process fluid pressure transmitter. One of thereasons for such significant cost is that in order to provide such arobust part, the coplanar pressure sensor module is constructed from acomplex stainless steel investment cast and machined part.

In accordance with embodiments of the present invention, the designconstraints of each portion of the coplanar pressure sensor module areconsidered individually, and tailored for specific needs. While theoverall assembly of a coplanar pressure sensor module in accordance withembodiments of the present invention may become more complex than priorart designs, such embodiments allow flexibility for differentapplications, and the ability to reduce costs on certain components,while potentially adding greater structural integrity to othercomponents.

FIG. 3 is diagrammatic perspective view of a prior art coplanar pressuresensor module and pressure flange in accordance with the prior art. Asillustrated in FIG. 3, pressure sensor module 102 is a unitaryinvestment cast stainless steel machined part. In contrast, FIG. 4illustrates an exploded diagrammatic perspective view of an improvedcoplanar pressure sensor module in accordance with one embodiment of thepresent invention. In this embodiments, module 192 includes a pluralityof components. Specifically, module 192 includes coplanar base 194 andhousing 196. The housing 196 is preferably threaded. Coplanar base 194and threaded housing 196 are joined together during module productionand the finished assembly is visually similar to prior art coplanarpressure sensor module 102. Coplanar base 194 and housing body 196 meetat an interface. As used herein, an interface is intended to mean apoint, line, plane or location where two different components meet.Coplanar base 194 may still be constructed from an investment cast, butit can also be forged or even cut from plate stock. Threaded housingbody 196 can be cast, forged, drawn, screw machined, or constructed frompipe stock. According to one embodiment, coplanar base 194 and threadedhousing body 196 may be constructed from different materials. Thisdifference may be manifested in different grades of stainless steel, forexample, coplanar base 194 may be constructed from 316 stainless steel,while threaded housing 196 may be constructed from 304 stainless steelor carbon steel. In embodiments where both components are constructedfrom the same basic material, such as stainless steel, the twocomponents can be welded together, using a method such as TIG welding.However, embodiments of the present invention also include constructingthreaded housing body 196 from a metal that is different than that usedfor the coplanar base, such as aluminum. In such embodiments, directwelding between a stainless steel coplanar base 194 and aluminumthreaded housing body 196 is not practical. Instead, the two componentsare preferably mechanically fixed together using shrink fitting andswaging. Swaging is a well-known process that is used to change (reduceor enlarge) the diameter of tubes and/or pipes.

As illustrated in FIG. 2, differential pressure sensor 140 may be of thetype that is generally of a cylindrical shape. In accordance with anembodiment of the present invention, coplanar base 194 may include abowl or dish-shaped depression 198 that allows pressure sensor 140 to bepositioned lower than prior art modules. This also reduces the overallheight of the entire assembly and further reduces material costs.Smaller physical size generally provides the advantage of less materialcost. In order to further reduce the size of coplanar pressure sensormodule assembly 192, circuit board 146, which is normally providedwithin the pressure sensor module, can be removed completely and placedin the upper electronics housing 101. This allows the housing height tobe reduced further. Such reductions in height and width enableutilization of thinner walls which reduces material costs further. Insome embodiments, a temperature sensor can also be provided within thethreaded housing body to help provide accurate temperature compensationfor pressure.

FIG. 5 is a cross sectional diagrammatic view of a coplanar pressuresensor module in accordance with another embodiment of the presentinvention. Module 292 differs from module 192 (shown in FIG. 4) in thatmodule 292 is constructed from three discrete components. Specifically,module 292 is constructed from coplanar base 294, tubular housing 296,and stiffener 300. In the embodiment illustrated in FIG. 5, the mostcomplex portion of the assembly is coplanar base 294. Preferably, thiscomponent is made relatively thinner, when compared to coplanar base194, and is formed using metal injection molding, or some other suitabletechnique that is adapted for the production of complex shapes andcomponents. Due to its thinner construction, base 294 is generally notstiff enough to form a robust seal to a process flange on its own.Instead, stiffener plate 300 is provided which bears against coplanarbase 294 at interface 302. Stiffener plate 300 includes a plurality ofbolt holes which preferably allow assembly 292 to be mounted to acoplanar manifold in exactly the same manner as prior art designs.However, if specific product applications require extremely highpressures, such considerations can be accommodated by simply providing astronger, or thicker stiffener plate 300.

Threaded housing body 296 preferably includes a lip 304 that is largerin diameter than aperture 306 through which tubular housing 296 passes.Thus, once stiffener plate 300 is secured in place, threaded housingbody 296 is sandwiched between stiffener plate 300 and base plate 294.Threaded housing body 296 preferably includes an o-ring recess 308 whichis configured to contain an elastomeric o-ring to seal threaded housingbody 296 to coplanar base 294 when threaded housing body 296 issandwiched between stiffener plate 300 and base plate 294.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. A coplanar process fluid pressure sensor module,the module comprising: a coplanar base having a pair of process fluidpressure inlets, each having an isolator diaphragm; a housing bodycoupled to the coplanar base at an interface between the coplanar baseand the housing body; and a differential pressure sensor operablycoupled to the pair of process fluid pressure inlets, and being disposedadjacent the coplanar base within the housing body; and a stiffenerplate having an aperture through which the housing body passes, thestiffener plate configured to clamp the housing body between itself andthe coplanar base.
 2. The coplanar process fluid pressure sensor moduleof claim 1, wherein the coplanar base is formed of a first metal and thehousing body is formed of a material different than the first metal. 3.The coplanar process fluid pressure sensor module of claim 2, whereinthe housing body is formed of a different grade of material than thefirst metal.
 4. The coplanar process fluid pressure sensor module ofclaim 3, wherein the first metal is stainless steel.
 5. The coplanarprocess fluid pressure sensor module of claim 4, wherein the coplanarbase and the housing body are coupled at the interface by a weld.
 6. Thecoplanar process fluid pressure sensor module of claim 2, wherein thehousing body is formed of a different metal than the first metal.
 7. Thecoplanar process fluid pressure sensor module of claim 6, wherein thedifferent material is aluminum.
 8. The coplanar process fluid pressuresensor module of claim 6, wherein the coplanar base is coupled to thehousing body at the interface via a shrink fit.
 9. The coplanar processfluid pressure sensor module of claim 6, wherein the coplanar base iscoupled to the housing body at the interface by swaging.
 10. Thecoplanar process fluid pressure sensor module of claim 2, wherein thecoplanar base includes a recess configured to receive the differentialpressure sensor.
 11. The coplanar process fluid pressure sensor moduleof claim 2, wherein the coplanar base is formed using metal injectionmolding.
 12. The coplanar process fluid pressure sensor module of claim2, wherein the housing body is fanned from casting.
 13. The coplanarprocess fluid pressure sensor module of claim 2, wherein the housingbody is forged.
 14. The coplanar process fluid pressure sensor module ofclaim 2, wherein the housing body is drawn.
 15. The coplanar processfluid pressure sensor module of claim 2, wherein the housing body isscrew machined.
 16. The coplanar process fluid pressure sensor module ofclaim 2, wherein the housing body is formed from pipe stock.
 17. Thecoplanar process fluid pressure sensor module of claim 1, wherein thehousing body includes a lip having a diameter greater than the aperture.18. The coplanar process fluid pressure sensor module of claim 1,wherein the housing body includes an o-ring surface to maintain ano-ring therein.
 19. The coplanar process fluid pressure sensor module ofclaim 1, wherein the differential pressure sensor is coupled directly toa circuit board disposed in an electronics housing separate from thehousing body.
 20. The coplanar process fluid pressure sensor module ofclaim 1, and further comprising a temperature sensor disposed within thehousing body.
 21. A coplanar process fluid pressure sensor module, themodule comprising: a steel coplanar base having a pair of process fluidpressure inlets, each having an isolator diaphragm; a cylindricalhousing body coupled to the coplanar base at an interface between thesteel coplanar base and the housing body, the cylindrical housing bodyhaving an externally threaded portion; a differential pressure sensoroperably coupled to the pair of process fluid pressure inlets, and beingdisposed proximate the coplanar base within the housing body; and astiffener plate having an aperture through which the housing bodypasses, the stiffener plate configured clamp the housing between itselfand the coplanar base.
 22. The coplanar process fluid pressure sensormodule of claim 21, wherein the cylindrical housing body is also formedof steel and is welded to the steel coplanar base.
 23. The coplanarprocess fluid pressure sensor module of claim 21, wherein thecylindrical housing body is formed of a different material than thesteel coplanar base.
 24. The coplanar process fluid pressure sensormodule of claim 23, wherein the cylindrical housing body is coupled tothe steel coplanar base by swaging.